One approach to treating a diseased tissue, such as a cancerous tumor, is surgical removal. However, surgical removal is invasive, and may be complicated and time consuming. Additionally, surgical treatment requires the selective treatment for each type of diseased tissues. Surgical treatment can also result in serious complications, such as from anesthesia. Clearly, a more comprehensive and non-invasive treatment of similar or better efficacy than surgical removal is desirable.
For example, high-intensity focused ultrasound (HIFU) has been demonstrated to be a safe modality to treat diseased tissue noninvasively. For example, HIFU has been used to treat liver cancer, ovary cancer, prostrate cancer, kidney cancer and testicular cancer. A HIFU system has an ultrasound transducer to transmit ultrasound waves which pass through the body skin of an animal and are focused on a to-be-treated tissue, such as a liver tumor. The incident focused ultrasound waves are absorbed and converted into heat at the focal point, known as the biological focal region (BFR), resulting in thermal ablation of the tumor cells. The high intensity ultrasound waves also further cause the tissue bubbles to oscillate steadily resulting in shear stresses that cause tumor cell damage, this is known as “stable cavitation”. The above-mentioned certain pressure threshold bubbles explode vigorously resulting in localized high acoustic pressure that causes tumor tissue damage, this is known as “inertial cavitation”.
However, although the transmitting power of the therapeutic transducer can be increased to improve the therapeutic efficiency, the normal tissue along the pathway of the ultrasound transmission is more likely to be burned in a high-intensity ultrasound environment. In addition, at present, when the HIFU technique is clinically applied to a hepatic tumor, the hepatic tumor is blocked by the ribs in the pathway of the ultrasound transmission, and the ultrasound transmission will heat and burn the rib tissue to cause damage of the ribs. Thus, before the therapy of HIFU, it is suggested to surgically remove the ribs in advance, in order to increase the energy deposition at the target location, shorten the treatment time and improve therapeutic effects. As a result, the noninvasiveness of HIFU treatment cannot be ensured, which is undesirable for the patients and doctors.
The above-mentioned problems have disadvantageously limited the use of the HIFU treatment as a technique for clinical practice. Therefore, the technical problems with respect to increasing the energy deposition at target location, effectively treating the deep-seated tumors without damaging the surrounding normal tissue (such as ribs) in the acoustic pathway, and treating a hepatic tumor that is blocked by the ribs without surgical removal of the ribs, need to be solved urgently.
It is therefore tried by the inventor to develop an ultrasound energy barrier for avoiding energy accumulation in a to-be-protected region during tumor treatment to solve the problems existing in the conventional HIFU treatment, as described above.